"The temptation to allow the problem of persuasion to overshadow the problem of knowledge"

From Daniel J. Boorstin's Hidden History, in the essay The Rhetoric of Democracy.

Democratic societies tend to become more concerned with what people believe than with what is true, to become more concerned with credibility than with truth

This manifests itself in the frequent overconcern in the political class about the nominal appearance of impropriety, conflict-of-interest, or of corruption coupled with an insouciance about the actual reality of those three fellow-travellers of politics.

And one might add to Boorstin's phrase, "more concerned with what people say they feel than with what they are willing to do".